Almost every country in the world has a railroad, one of our most important means of transportation. Laid end-to-end, the tracks of the world's railroads would stretch three times the distance from the earth to the moon. Only ships carry heavier cargoes for longer distances. Only airplanes transport the public faster than railroads.

Crude forms of railroads existed in Europe 400 years ago to haul wagon loads of coal from underground mines. Two wooden rails laid side-by-side extended from the entrance down onto the floor of the mine. Men or horses pulled the wagon, which moved more easily on the rails than on muddy and rutted ground. Gradual improvements were made over the next two centuries. The rails were extended to run above as well as below ground. Wood was reinforced, then entirely replaced, by iron. But the length of these primitive railroads remained very short, for the means to propel the wagon continued to require human or animal labor.

Steam

The age of the modern railroad dawned with the invention of the steam engine. In 1804 a high-pressure steam engine was mounted upon a four-wheeled undercarriage designed to run along a track, and carried 9 metric tons, 5 wagons and 70 men. In 1830 the first passenger service was inaugurated. The "iron horse" had arrived.

A steam engine derives its power by producing heat from the burning of coal or oil in a firebox. The heat turns the water in a locomotive's boiler into steam, which is fed into cylinders. There, the pressure produced by the steam pushes against disks called pistons. The pistons are connected to rods which move the wheels.

But the steam locomotive has several disadvantages. A lot of time is required to light the fire and heat the boiler so that steam can be produced. And although speed increased to 50-60 miles per hour by the end of the 19th century, the steam engine is not fuel efficient. It requires large amounts of coal to produce and maintain power, and most of the heat is wasted.

Less than 50 steam locomotives, most of them tourist attractions, still operate in the United States. Steam power has been replaced by either the diesel or the electric locomotive.

Diesel

In comparison with the steam locomotive, the diesel engine has several advantages. It is more fuel efficient, requires less servicing, and costs less to maintain. A diesel locomotive can make longer runs, as well as starting, stopping, and speeding up faster than the steam locomotive.

The diesel is an internal combustion engine. That is, power is derived by burning an explosive mixture of gases. The diesel engine varies from the conventional internal combustion engine in that the fuel is not detonated by a spark but by the heat produced when air is compressed in a cylinder. When the air is compressed, its temperature rises. The resulting heat ignites fuel that has been injected into the cylinder. The power produced during this process is transmitted to the driving wheels.

There are three types of diesel locomotives: (1) diesel-electric, (2) diesel-hydraulic, and (3) diesel-mechanical. Each transmits power from the engine to the driving wheels in different ways. Almost all locomotives in the United States today are diesel-electric.

The diesel engine was invented in 1892, and the diesel locomotive was introduced experimentally in 1923. The first passenger diesel went into operation in 1925 and the first freight diesels went into service in 1940. Today there are over 20,000 diesel locomotives operating in the United States.

Electric

Electric locomotives were introduced in the late 19th century. Unlike diesels, electric locomotives do not generate their own power - they use power supplied by an electrical power plant that may be miles away. An electric locomotive, therefore, needs special wires or rails from which it can get power.

Many electric locomotives use a "third rail" which runs parallel to the regular rails on which the train travels. A metal device called a contact shoe is attached to the locomotive. The shoe slides along the third rail and picks up electricity from it.

Electric locomotives can draw large amounts of power from the central plant, while diesel locomotives are limited to the power they can produce from the fuel they carry. Electric locomotives are also quiet and produce no smoke or exhaust fumes. Electric locomotives can start and stop more quickly than diesels. Finally, electricity can be produced from a variety of fuels - coal, gas, oil, water, or atomic power. Diesel locomotives can only run on diesel oil, which may become scarce and thus more costly.

Europe's train systems were converted to electricity early in the 20th century. Although only about 100 electric railroads operate in the United States today, electrification may become widespread in the next century.

Tracks

Unlike ships, airplanes and automobiles, trains traveling on railroads are not steered; they are guided by tracks along a permanent route - a "rail road."

Most track is made up of two steel rails running parallel and fastened lengthwise to a series of cross ties. The wheel-and-axle assemblies of locomotives and cars are specially designed to run on the track. Each wheel has a flange (rim) around its inner edge. The flanges on each pair of wheels guide the wheels along the track. Switches - short movable rails that turn on pivots - are built into the track where it meets other tracks. By turning a switch, a train can move from one track onto another.

The roadbed on which tracks are laid is specially prepared to make the ride as level and smooth as possible, and to hold the ties in place and keep the track stable. The route of the track is planned to minimize steep grades and curves, which reduce a train's speed and/or load.

In many cities the space required of a roadbed has led to its being elevated above or submerged below ground. Yet the size and weight of traditional trains make a heavy demand on land, material, labor and energy.

Competition

The advent of the automobile (and airplane) has reduced reliance on passenger trains, particularly in the United States. While people in China, India, Japan, and most of Europe still rely heavily on trains for transportation, railroads now carry less than 1% of all U.S. intercity travel.

The automobile's appeal is that it's personal. You travel when you want and where you want - no timetables, no tracks. But air pollution, road surface space requirements, and gridlock form the negative impact of the automobile to the environment and society.

Technical innovations that address these transportation issues are now being designed, implemented and evaluated. Hybrids that accentuate the positives of railroad and automobile travel, while minimizing their negatives, are explored in our "Monorail" section.

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Last modified: Sat Jun 28 10:10:38 PDT 1997

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